Question

I have two different list types. I need to remove the elements from list1 that is not there in list2 and list2 element satisfies certain criteria.

Here is what I tried, seems to work but each element is listed twice.

   var filteredTracks =
                    from mtrack in mTracks 
                    join ftrack in tracksFileStatus on mtrack.id equals ftrack.Id
                    where mtrack.id == ftrack.Id && ftrack.status == "ONDISK" && ftrack.content_type_id == 234
                    select mtrack;

Ideally I don’t want to create a new copy of the filteredTracks, is it possible modify mTracks in place?

Answer 1

If you’re getting duplicates, it’s because your id fields are not unique in one or both of the two sequences. Also, you don’t need to say where mtrack.id == ftrack.Id since that condition already has to be met for the join to succeed.

I would probably use loops here, but if you are dead set on LINQ, you may need to group tracksFileStatus by its Id field. It’s hard to tell by what you posted.

As far as “modifying mTracks in place”, this is probably not possible or worthwhile (I’m assuming that mTracks is some type derived from IEnumerable<T>). If you’re worried about the efficiency of this approach, then you may want to consider using another kind of data structure, like a dictionary with Id values as the keys.